Electromagnetic interference (EMI) shielding materials are disclosed in U.S. Pat. Nos. 4,935,296 and 5,089,326. The '296 patent discloses a composite containing an EMI shieldingly effective amount of metal-coated fibers and details of such fibers can be found in U.S. Pat. Nos. 4,738,896; 4,759,950; 4,789,563 and 4,839,402.
Radar absorptive coating materials are disclosed in U.S. Pat. Nos. 3,599,210 and 3,843,593. The '210 patent discloses a coating containing fibers cut to a length of one-half wavelength of the anticipated radar frequency with the fibers being insulated along their lengths by thinly bonding a dielectric, low loss material such as untilled epoxy, pure resin or varnish and the fibers are randomly dispersed within a solid matrix of resinous material. The '593 patent discloses a coating containing iron pigment in a resin matrix.
U.S. Pat. No. 4,983,456 discloses electrically conductive laminates, conductive coatings, conductive adhesives, conductive inks, conductive gaskets and conductive caulking and sealing compounds wherein metal coated fibers are utilized. The '456 patent further discloses polymeric material convertible by heat or light, alone or in combination with catalysts, accelerators, cross-linking agents, etc., can be combined with the composite fibers. The fibers include a semi-metallic core made of carbon, boron or silicon carbide and an electrically and/or thermally conductive layer of at least one electro-depositable metal such as nickel, silver, zinc, copper, lead, arsenic, cadmium, tin, cobalt, gold, indium, iridium, iron, palladium, platinum, tellurium, or mixtures thereof.
The following U.S. patents relate generally to methods of mixing filler or fibers and resin and/or applying a mixture of resin and filler/fiber material onto a substrate. The patents include U.S. Pat. Nos. 2,923,934; 2,929,436; 3,599,210; 4,325,849; 4,360,440; 4,474,685; 4,534,998; 4,862,713; 4,935,296; and 4,983,456. The foregoing patents, however, fail to appreciate the importance of avoiding breakage of fibers during mixing of the fibers with a resin matrix and during applying the mixture to a substrate. For instance, with respect to electromagnetic attenuating materials, such breakage could result in fibers having lengths that reduce, and conceivably even eliminate the desired electromagnetic attenuating property.